Goniochromaticity is the effect of perceived color varying as the angle of illumination or observation varies. Goniochromatic pigments are used, for example, in automotive coatings, decorative coatings, plastic pigmentation, printing inks (security inks in particular), textiles and cosmetics. Their optical effect results from the directional reflection of light from predominantly sheet-like particles that conventionally are metallic or that have a structured refractive index contrast, the length scale of which is comparable to the wavelength of light. According to the nature of the pigment particles, the pigments are known as metallic effect pigments (for example, aluminum, zinc, copper or alloys thereof) or interference pigments (for example, based on titanium dioxide-coated mica, such as muscovite, phlogopite and biotite).
As a result of the incident light being reflected directionally by the predominantly sheet-like particles, color effect pigments that are oriented, for example, in a coating, exhibit goniochromaticity; that is, their perceived color (lightness and/or hue and/or chroma) varies with the angle of illumination or observation.
There is a need for durable goniochromatic materials that can be produced in particulate form and that are suitable for use as colorants with minimal haze.